Combustion control



1935. A. G. BLODGETT 2,026,159.

V COMBUSTION CONTROL Filed Sept. 19, 1934 Patented Dec. 31, 19 35 UNITED STATES PATENT OFFICE Riley Stoker Corporation, Worcester, Mass., a.

corporation of Massachusetts Application September 19, 1934, Serial No. 744,630 17 Claims. (Cl. 236-26) This invention relates to combustion control, and more particularly to a method and apparatus for controlling combustion in furnaces of the induced draft type, in which the flow of the air for combustion is brought about by a suction fan or a stack connected to the outlet of the furnace, as distinguished from forced draft furnaces having provision for supplying the air at a pressure above that of the atmosphere.

It has previously been proposed to control the supply of fuel and the position of the furnace outlet damper in accordance with the demand for heat. This method cannot maintain the fuel-air ratio with the accuracy required in burning fuels such as pulverized coal, oil or gas, which burn in suspension, for the rate of air supply depends upon many factors other than the damper position. For example, the rate of air supply will vary with the available stack draft, which is a. function of weather conditions, number of furnaces in operation, etc. It has furthermore been proposed in steam boiler furnaces to control the furnace outlet damper by apparatus responsive to both the steam pressure and the drop'in the pressure of the gas as it flows in contact with the surfaces of the boiler. In a system of this type the fuel-air ratio will be affected by such factors as the condition of the boiler bafiles, the quantity of soot and slag accumulated on the boiler tubes, coke deposits in the burner passages, etc. As a result it is not possible to maintain efficient combustion continuously.

It is accordingly one object of the invention to provide an improved method of control whereby highly eflicient combustion may be maintained in furnaces of the induced draft type.

It is a further object of the invention to provide improved automatic apparatus for controlling the fuel and air supplies ininduced draft furnaces, and particularly in steam boiler furnaces fired with fuels which burn in suspension.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts and the steps of'the process set forth in the specification and covered by the claims appended hereto. 7

In accordance with my invention I regulate the fuel supply to an induced draft furnace in response to variations in the demand for heat, and I regulate the discharge ofthe gases from the furnace in response to variations in the demand for heat and in the rate of air flow into the furnace. In a steam boiler furnace I preferably use the steam pressure as an indication of the demand for heat. The discharge of the furnace gases is preferably regulated by means of an outlet damper.

Referring to the drawing illustrating one embodiment of the invention, and in which like reference numerals indicate like parts,

The single figure shown is a somewhat diagrammatic elevation of a steam boiler furnace and associated apparatus, certain parts being broken away for clearness of illustration.

The embodiment illustrated comprises a fur- 10 nace H! of the induced draft type having a gas outlet or uptake ll provided with a damper l2. The uptake l I is connected to a suction fan 14 having a discharge duct l5 which may lead to a suitable stack (not shown). It will be apparent 15 that if the stack provides sufiicient draft the fan may be omitted. Associated with the furnace I0 is a water tube steam boiler I6 of suitable construction provided with a steam delivery pipe I1. Thefurnace isarranged for firing with pulverized 20 coal, and for this purpose I have shown a suitable pulverizer 19 having its delivery pipe 20 connected to a burner 21- on the wall of the furnaces. The pulverizer is provided with a regulatable feeding mechanism 23 which is supplied with coarse coal 25 from an overhead bunker 24 through a downspout 25. The burner 21 is provided with an entrance duct 21 through which the air for combustion is drawn into the furnace under the influence of the draft set up by the fan I4.

The feeding mechanism 23 is' regulated automatically in accordance with the demand for heat, and as an indication of the demand I preferably utilize the pressure of the steam generated. In the embodiment illustrated the steam pressure in the pipe I! is transmitted through a pipe 29 to an automatic regulator 30 of the compensating type, one suitable construction being disclosed in the patent to Paul 0. Temple No. 1,890,472, granted December '13, 1932. The regulator is connected 40 to'the feeding mechanism 23 by means of a link 32, a bell-crank 33, and a rod' 34.

The uptake damper I2, which controls the dischargeof the gases from the furnace, is regulated automatically in accordance with both the demand for heat and the rate of air flow into the furnace. For this purpose I preferably utilize a regulator 36 of the type shown in the patent to Paul 0. Temple, No. 1,992,048, granted February 19, 1935. This regulator comprises a pilot valve mechanism 31 supplied with fluid under pressure by a pipe 31' and connected by pipes 38 with. a hydraulic motor 40 which serves to actuate the operating arm 4| of the uptake damper l2. The pilot valve mechanism 31 is actuated by a lever 43 which is controlled by a flexible pressure-responsive diaghragm 44 loaded by means of a tension spring 45. The spring 45 is connected at its upper end to a nut 41 supported on a vertically slidable screw 48. The upper end of the screw 48 is provided with a flange 49 which rests on a collar 50, this collar being connected by links 52 to a pivotally mounted lever 53 having a cam roller 54 on one end. The roller 54 engages a cam 5.5 mounted. on a shaft 51 to which is secured an operating arm 58. It will be apparent that as the cam 56 is turned. by means of the arm 58, the screw 48 will be moved vertically, thus changing the tension of the spring 45. The spring tension can also be adjusted by rotating the screw 48 manually, thus raising or lowering the nut 41.

In order that the regulator 36 may respond to variations in the demand for heat, I connect the steam pressure regulator 30 to the arm 58. by means of a link 6. With this construction, a change in steam pressure will cause the regulator 3!} to move the arm 58 and readjust the spring 45.

In order that the regulator 36 may respond to variations in'the rate of air flow into the furnace, I subject the diaphragm 44 to an effective fluid pressure which is an indication of said rate of flow. For this purpose I prefer to utilize a Pitot tube 82 mounted in the burner air duct 21 and connected to. the space above the diphragm 44 by means of a pipe 62. The space below the diaphragm is connected to the duct 21 by means of a pipe 64. The entrance to the duct 21 is preferably formed with an inwardly directed flange 66 which restricts the duct area and thus increases the velocity of the air adjacent to the Pitot tube 62, which is located a short distance posterior to the flange. Inthe case of a comparatively short duct Iv prefer to connect the pipe64, to the duct at a point between the flange and the Pitot tube.

It will be noted that the operating lever 43 of the pilot valve mechanism 31 is subjected to two opposing forces. The first of these forces is provided by the spring 45 and is a function of the demand for heat as indicated by the steam pressure and the resultant position assumed by the regulator 38. The second of these forces is rovided by the effective fluid pressure on the diaphragm 44 and is a function of the rate of air flow'into the furnace as indicated by the. dy namic and static pressures of the air measured by the Pitot tube. Since these two forces oppose each other, the lever 43. will be actuated in accordance with their differential.

The operation of the invention will now be apparent from the above disclosure. Under steady loadjconditions the steam pressure will remam uniform, and the regulator 36 will hold the feeding" mechanism 23 in position to maintain the supply of coal at a rate commensurate with the demand for heat. The forces on the lever 43,'will be balanced, and the motor 40 will hold the damper 12 in the proper position to maintain an established air flow in the duct 21 in the correct relationship with thecoal supply. If the air flow should start to change, perhaps as a result of varying stack draft, slagging of boiler tubes, leading baffles, or coke depositsin the burner, theeeff ctive pressure transmitted to the diaphragm 44 through the pipes 63 and 64wi1l.

change, upsetting the, balance of forceson the lever 43, and causing a readjustment of the m r 9 raters il ew t ss jei f Q f the demand for heat should change, the resultant change in steam pressure will cause the regulator 36 to readjust the feeding mechanism 23 as well as the tension of the spring 45. This will upset the balance of forces on the lever 43, and the damper l2 will consequently be readusted until a balanced condition is restored by a change in the air flow into the furnace and a resultant change in the eifective pressure on the diaphragm 44. Thus the correct fuel-air ratio will be maintained.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. A combustion control system for an induced draft furnace comprising means for regulating the fuel supply in accordance with the demand for heat, power actuated means for regulating the discharge of the gases from the furnace, a fluid pressure responsive device to control the power actuated means, means to subect the fluid pressurerjesponsive device to an effective fluid pressure which is a function of the rate of air flowin'to the furnace, and means to subject the fluid pressure responsive device to a force which opposes the fluid pressure thereon, said force being a function 'of the demand for heat.

2. A combustion control system for an induced draft furnace comprising power actuated means for regulating the discharge of the gases 0 from the furnace, means including a flexible diaphragm to control the power actuated means, means to subject the diaphragm to an effective fluid'p-ressure which is a function of the rate of air' flow into the furnace, a spring connected. to

the diaphragm to support the same against the fluid pressure, and means to regulateboth the fuel supply and'the force of the. spring in accordance with the demand for heat.

3. The method of controlling combustion in a furnace which comprises regulating the fuel supply inaccordance with the demand for heat, maintaining a suction at the furnace outlet, inducing afl'o'w of "air into the furnace solely by the effect of said suction, andregulating the discharge (if the gases from theffurnace in accordance with both the demand for heat and the rate of air flow into the furnace.

4. The method of controlling combustion in a steam generating furnacewhich comprises regt ulat'ing "the fuel supply inv accordance with the steampressure, maintaining a suction at the furnace outlet, inducing a. flow of air into the furnace solely by the effect of said suction, and regulating the discharge of the gases from the fur- 7 na'ce'in accordance with both the steam pressure and the rate of air flow into the furnace.

5. The method of controlling combustion in a steam generating furnacehaving an outlet damper which comprises regulating the fuel supply in accordance with 'the demand for heat, maintaining a suction at the furnace outlet, inducing a flow of air into the furnace solely by the effect of said suction, and regulating the outlet damper in accordance with both the demand for heat and the rate of air flow into the furnace.

6. The method of controlling combustion in a furnace having a burner and arranged for burning fuel. in suspension which comprises regulating the. fuel supply to the burner in accordance withthe demandfor heat, maintaining a suction at the. furnace outlet, inducing a flow of air through the, burner solely by the effect of said suction, and regulating the discharge of the gases from the furnacein accordance with both, the de- 75,

mand for heat and the rate of air flow into the burner.

7. The method of controlling combustion in a furnace which comprises regulating the fuel supply in accordance with the demand for heat, maintaining a suction at the furnace outlet, inducing a flow of air into the furnace solely by the effect of said suction, regulating the discharge of the gases from the furnace to maintain an established rate of air flow into the furnace, and varying said established rateof air flow in accordance with variations in the demand for heat.

8. The method of controlling combustion in a furnace which comprises regulating the fuel supply in accordance with the demand for heat, maintaining a suction at the furnace outlet, inducing a flow of air into the furnace solely by the effect of said suction, providing a force which is a function of the demand for heat, providing a second force which is a function of the rate of air flow into the furnace, and regulating the discharge of the gases from the furnace in accordance with the differential of said forces.

9. The method of controlling combustion in a furnace having an outlet damper which comprises regulating the fuel supply in accordance with the demand or heat, maintaining a suction at the furnace outlet, inducing a flow of air into the furnace solely by the effect of said suction, providing a force which is a function of the demand for heat, providing a second force which is a function of the rate of air flow into the furnace, and regulating the outlet damper in accordance with the differential of said forces.

10. A combustion control system for a furnace having an air inlet communicating with the at mosphere comprising means for regulating the fuel supply in accordance with the demand for heat, means to maintain a suction at the furnace outlet and thereby induce a flow of air through the inlet, and means for regulating the discharge of the gases from the furnace in accordance with both the demand for heat and the rate of air flow through the inlet.

11. A combustion control system for a steam generating furnace having an air inlet communicating with the atmosphere comprising means for regulating the fuel supply in accordance with the steam pressure, means to maintain a suction at the furnace outlet and thereby induce a flow of air through the inlet, and means for regulating the discharge of the gases from the furnace in accordance with both the steam pressure and the rate of air flow through the inlet.

12. A combustion control system for a furnace having an outlet damper and an air inlet communic'ating with the atmosphere comprising means for regulating the fuel supply in accordance with the demand for heat, means to maintain a suction at the furnace outlet and thereby induce a flow of air through the inlet, and means for regulating the outlet damper in accordance with both the demand for heat and the rate of air flow through the inlet.

13. A combustion control system for a furnace having a burner and arranged for burning fuel in suspension comprising means for regulating the fuel supply to the burner in accordance with the demand for heat, means to maintain a suction at the furnace outlet and thereby induce a 5 flow of air through the burner, and. means for regulating the discharge of the gases from the furnace in accordance with both the demand for heat and the rate of air flow into the burner.

14. A combustion control system for a furnace having an air inlet communicatingwith the atmosphere comprising means for regulating the fuel supply in accordance with the demand for heat, means to maintain a suction at the furnace outlet and thereby induce a flow of air through the inlet, means for regulating the discharge of the gases from the furnace in accordance with the rate of air flow through the inlet and tending to maintain an established rate of air flow, and means for varying the rate of air flow to be maintained in accordance with variations in the demand for heat.

15. A combustion control system for a furnace having an air inlet communicating with the atmosphere comprising means for regulating the fuel supply in accordance with the demand for heat, means to maintain a suction at the furnace outlet and thereby induce a flow of air through the inlet, means providing a force which is a function of the demand for heat, means providing a second force which is a function of the rate of air flow through the inlet, and means for regulating the discharge of the gases from the furnace in accordance with the differential of said forces.

16. A combustion control system for a furnace having an air inlet communicating with the atmosphere comprising means for regulating the fuel supply in accordance with the demand for heat, means to maintain a suction at the furnace outlet and thereby induce a flow of air through the inlet, means providing a force which is a function of the demand for heat, means providing a second force which is a function of the rate of air flow through the inlet, power actuated means for regulating the discharge of the gases from the furnace, and means for controlling the power actuated means in accordance with the differential of said forces.

17. A combustion control system for a furnace having an air inlet communicating with the atmosphere comprising means for regulating the fuel supply in accordance with the demand for heat, means to maintain a suction at the furnace outlet and thereby induce a flow of air through the inlet, means providing a force which is a function of the demand for heat, means providing a second force which is a function of the differential of the dynamic and static pressures of the air flowing through the inlet, and means for regulating the discharge of the gases from the furnace in accordance with the differential of said forces.

ALBERT G. BLODGETT. 

